1. Field of the Invention
The present invention relates to an automatic transmission to be mounted on a vehicle. More particularly, the present invention relates to a continuously variable hydrostatic transmission in which a swashplate type hydraulic pump of a fixed displacement and a swashplate type hydraulic motor of a variable displacement are connected via a hydraulic closed circuit. The present invention further relates to a method of controlling a movable swashplate of a transmission.
2. Background Art
A conventional continuously variable hydrostatic transmission is applied to a transmission of a motorcycle. Japanese Registered Patent No. 2527199 discloses a method of controlling a such continuously variable hydrostatic transmission by comparing a real rotational speed (hereinbelow referred to as xe2x80x9cNexe2x80x9d), based on a rotational speed Ne of a crank shaft or the like, with a target rotational speed Ne, determined by preset conditions by a controller, and adjusting an inclination angle of a moveable swashplate, thereby controlling an output.
Japanese Unexamined Patent Publication No. H8-82354 discloses a method of performing a step-by-step gear ratio control similar to that performed by a manual multi-stage transmission by a continuously variable transmission (hereinbelow, called stage transmission).
A transmission gear ratio in a conventional continuously variable transmission having a motor-driven changing mechanism is corrected by shifting a shift position to an extreme position in response to each shift-up (or shift-down) command, and using the value of a spindle angle at the time of the extreme position as a correction value. The correction is performed sequentially when a shift command is generated (hereinbelow referred to as xe2x80x9csequential correctionxe2x80x9d). With respect to correction of the angle of a swashplate of a continuously variable hydrostatic transmission, when a vehicle is stopped, the swashplate of the continuously variable hydrostatic transmission is on a maximum deceleration position (LOW ratio) side. Consequently, the swashplate does not reach a minimum deceleration position ratio (TOP ratio) depending on a driving state after the vehicle starts, and the angle of the swashplate is not corrected.
In the case where the correction is not performed, the value of the ratio of the continuously variable hydrostatic transmission becomes unclear. In the case of using a continuously variable hydrostatic transmission system as a stage transmission, the gear ratio before correction and that after the correction are different from one another. Consequently, it is difficult to perform accurate sequential correction.
In light of the shortcomings of the conventional art, it is an object of the invention to accurately correct the gear ratio in a continuously variable transmission.
According to a first aspect of the invention, a continuously variable transmission is provided which determines either a target engine speed or a target gear ratio on the basis of a throttle angle, a vehicle speed, and an engine speed. The continuously variable transmission further controls a gear ratio of the continuously variable transmission on the basis of the target engine speed or the target gear ratio. A storage device is provided for storing a minimum shift position and a maximum shift position of a transmission control member of the continuously variable transmission.
According to the first aspect of the invention, when a correcting operation of storing the positions is performed once before driving, the gear ratio is therefore corrected on the basis of the position information. This renders a correcting operation after driving unnecessary, and the correction of the gear ratio in a continuously variable transmission is thereby facilitated.
According to a second aspect of the invention, a maximum deceleration position and a minimum deceleration position of a continuously variable transmission are determined on the basis of prestored minimum and maximum shift position data of the transmission control member of the continuously variable transmission.
According to the second aspect of the invention, the maximum deceleration position (LOW ratio) and the minimum deceleration position (TOP ratio) of a continuously variable transmission can be determined on the basis of the correction data. Consequently, unlike a conventional technique, a member in addition to the continuously variable transmission for, for example, measuring a spindle angle of an electric changing mechanism, is not required. This eases the correcting control, and the control of correcting the gear ratio in a continuously variable transmission is facilitated.
According to a third aspect of the invention, a transmission control method of a continuously variable transmission switches the continuously variable transmission to a shift position in stages. The gear ratio corresponding to a shift position in stages on the basis of gear ratio data corresponding to prestored maximum deceleration position and minimum deceleration position of the continuously variable transmission.
According to the third aspect of the invention, the gear ratio of each stage in the case of shifting a gear in stages can be determined based on the correction data, so that the gear shift in stages in a continuously variable transmission can be performed accurately and easily.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.